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Biomedical subjects

R S Gupta

Publications and source records attributed to R S Gupta.

At least 217 records · Page 12Linked to original sources
PubMed1982

Human fibroblast strains showing increased sensitivity or resistance to ethidium bromide.

The sensitivity of a number of human fibroblast cell strains towards the DNA intercalating and mutagenic agent ethidium bromide has been examined. Among the cell strains investigated, 3 were of fetal origin, 6 from clinically normal adult persons, 2 from Lesch-Nyhan individuals and 1 each from persons with 3 genetic disorders, xeroderma pigmentosum, Fanconi anemia and Bloom syndrome, which are known to predispose to cancer. Results of our studies show that cells derived from 2 otherwise normal individuals exhibits a marked sensitivity towards ethidium bromide as compared to the rest of the group. At the same time all 3 cell strains of fetal origin were found to be highly resistant to killing by this agent. These results are discussed in relation to the toxic/mutagenic effects of ethidium bromide.

Adolescent↗
PubMed1982

Antispermatogenic/antiandrogenic properties of solasodine (C27H43O2N) obtained from solanum xanthocarpum berries on the male genital tract of dog (Canis-familiaris). A histophysiological approach.

Chronic administration of solasodine (20 mg/kg alt. day for 30 days) caused testicular lesions resulting in a severe impairment of spermatogenic elements. The epididymides were devoid of spermatozoa. Total protein, sialic acid and glycogen contents of the testis and epididymis were reduced significantly whereas the testicular cholesterol was elevated. Acid Phosphatase enzyme activity of the testes was low after solasodine treatment. Serum enzymes (SGPT, alkaline phosphatase) serum protein, triglycerides, non esterified fatty acid levels were in normal range when compared with their own controls. Cholesterol and phospholipid levels were elevated after solasodine treatment to intact dogs. Reduced androgen production was reflected in low levels of sialic acid in the testes and epididymides and reduced Leydig cell nuclei. Castration alone brought about reduction in size of the epididymis. Castration followed by solasodine treatment caused epididymal degeneration. Simultaneous administration of TP to solasodine treated castrated dogs failed to stimulate the epididymal growth. Antispermatogenic/antiandrogenic activity of the compound solasodine is discussed. Solasodine administration in dogs definitely rendered the male infertile as evidenced by the absence of sperms in the cauda epididymis and ductus deferens.

Animals↗
PubMed1981

Resistance to the microtubule inhibitor podophyllotoxin: selection and partial characterization of mutants in CHO cells.

Stable mutants two- to fourfold more resistant to the microtubule inhibitor podophyllotoxin (PodRI) have been selected in a single step in Chinese hamster ovary (CHO) cells. Mutants showing higher levels of resistance to the drug can be obtained in a second-step selection using the PodRI mutants (PodRII class). Prior treatment of cells with the mutagen ethylmethane sulfonate markedly enhanced the frequency of both PodRI and PodRII mutants in culture. The spontaneous rate of mutation of PodRI as determined by fluctuation analysis was found to be 1 - 2 x 10(-5) and 4 x 10(-7) mutations/cell/generation at 20 and 30 ng/ml podophyllotoxin, respectively. Somatic cell hybrids between PodRI x PodS and PodRII x PodS showed intermediate levels of resistance to the drug, indicating that the PodR phenotype behaves codominantly under these conditions. Cross-resistance studies with various PodRI and PodRII mutants show that they are not cross-resistant to other microtubule inhibitors, e.g., colchicine, colcemid, griseofulvin, vinblastin, that have been examined, or to a compound such as VP16-213, which is a podophyllotoxin derivative which lacks microtubule inhibitory activity. These results indicate that the lesion in PodR mutants is highly specific and probably does not involve a permeability alteration.

Animals↗
PubMed1981

Podophyllotoxin resistance: a codominant selection system for quantitative mutagenesis studies in mammalian cells.

Mutants resistant to the microtubule inhibitor podophyllotoxin (PodR), a codominant marker, can be readily selected in various mammalian cell lines such as, CHO, HeLa, mouse L cells, Syrian hamster cells (BHK21) and a mouse teratocarcinoma cell line OC15. In CHO cells, the recovery of PodR mutants is not affected by cell density (up to 1 X 10(6) cells per 100-mm diameter dish), and after treatment with the mutagen ethyl methanesulfonate maximum mutagenic effect is achieved after a relatively short expression time (40-48 h). The frequency of PodR mutants in various cell lines increased in a dose-dependent manner in response to treatment with the mutagens ethyl methanesulfonate and N-methyl-N'-nitro-N-nitrosoguanidine. The PodR selection system thus provides a new genetic marker which should prove useful in studies of quantitative mutagenesis in mammalian cells.

Animals↗
PubMed1980

Pactamycin resistance in CHO cells: morphological changes induced by the drug in the wild-type and mutant cells.

Stable mutants resistant to pactamycin (PacR), a polypeptide chain initiation inhibitor, have been selected in a single step in Chinese hamster ovary (CHO) cells. The sensitivity of protein synthesis in mutant cell extracts to pactamycin indicates that resistance involves an alteration in the permeability of this drug. The failure of PacR mutants to show cross-resistance to other compounds provides further indication that the lesion is presumably specific for pactamycin. Cell hybrids formed between PacR X PacS lines show intermediate sensitivity towards pactamycin, suggesting that the PacR lesion behaves codominantly under these conditions. In the presence of subinhibitory concentrations of pactamycin, CHO cells, which are normally short, polygonal and disoriented, became greatly elongated and aligned themselves in parallel fashion to produce highly oriented colony morphologies, reminiscent of normal diploid fibroblasts. This effect of pactamycin on cellular morphology was seen much more clearly with the PacR mutants, although somewhat higher concentrations of the drug were required to produce this change.

Animals↗
PubMed1980

Senescence of cultured human diploid fibroblasts. Are mutations responsible?

Two predictions of the error/mutation hypothesis of cellular senescence (Orgel, '73) namely,a) exponential accumulation of somatic mutations during the replicative lifespan and b) shortening of culture lifespan upon treatment with mutagens have been examined experimentally in a strain of cultured human diploid fibroblasts. Our studies show that as cells traverse the replicative lifespan (from 10 to 75 mean population doublings (MPD); total lifespan congruent to 95 MPD), no rapid and exponential increase occurs in the accumulation of mutations measured by the frequencies of Thgr(thioguanine resistance) and Dipr (diphtheria toxin resistance) mutants. Furthermore, repeated cycles of treatment (from 1- to 14-times) of human fibroblasts with two mutagens, ethyl methane sulfonate (EMS) and N-methyl-N' nitro-nitrosoguanidine, which led to a marked increase in the mutation frequency for the Dipr marker (congruent to 100-fold), failed to shorten the lifespan of cultured fibroblasts. On the contrary, repeated mutagen treatment (12 times with EMS) prolonged the lifespan of one replicative culture (110 MPD versus 94--98 MPD). These results strongly indicate that mutations are unlikely to be the primary event in cellular senescence and suggest instead that senescence is probably controlled by one or more (specific) gene(s) whose expression can be modified by mutations.

Cell Line↗
PubMed1980

A novel synergistic effect of alanosine and guanine on adenine nucleotide synthesis in mammalian cells. Alanosine as a useful probe for investigating purine nucleotide metabolism.

A novel synergistic effect of the antitumor agent alanosine (2-amino-3-(hydroxynitrosoamino) propionic acid), which specifically inhibits the enzyme adenylosuccinate synthetase (ASS) and guanine on the growth of Chinese hamster ovary (CHO) cells and human diploid fibroblasts (HDF) has been observed. In the presence of subinhibitory concentrations of alanosine, both CHO cells and the HDF show excessive sensitivity to exogenous guanine--a phenotype which closely resembles that seen with some of the mutants containing reduced enzymatic activity of ASS. The growth inhibitory effects of alanosine, or alanosine and guanine, on CHO cells are completely reverted by the addition of adenine to the culture medium, and the synergistic effect of guanine is not observed in mutants which lack the enzyme hypoxanthine-guanine phosphoribosyl transferase. These resuls suggest that guanine nucleotides exert a regulatory effect on the activity of the enzyme adenylosuccinate synthetase. The ability to confer the guanine-sensitive phenotype and its modulation by subinhibitory concentrations of alanosine in different cell types indicates that alanosine provides a useful probe for investigating the regulation of purine nucleotide metabolism in mammalian cells.

Adenine↗
PubMed1980

Studies on temperature-sensitive mutants of Chinese hamster ovary cells affected in DNA synthesis.

DNA synthesis in two mutants of Chinese hamster overy cells, ts 13A and ts 15C, which were temperature sensitive for growth, was found to be shut off rapidly at the nonpermissive temperature. The mutants did not complement each other and the ts lesion was not located on the X chromosome. Both isolates were found to be considerably more sensitive to the alkylating agents, ethylmethanesulfonate (EMS) and methylmethanesulfonate (MMS), as compared to the parental cells, but showed normal sensitivity to UV irradiation. The mutants also showed interesting differences in their response to EMS-induced mutation frequencies at the ouabain-resistant and thioguanine-resistant loci. At high survival (50%) the frequencies of mutations at these genetic loci were markedly low in the ts mutants as compared to the parental cells. In ts+ revertants isolated from the mutants, the ts phenotype and the increased sensitivity to EMS and MMS were affected simultaneously, indicating that both these characteristics resulted from a single genetic lesion.

Alkylating Agents↗
PubMed1980

Random segretation of multiple genetic markers from CHO-CHO hybrids: evidence for random distribution of functional hemizygosity in the genome.

The linkage relationship between various recessive markers isolated in Chinese hamster ovary (CHO) cells has been investigated. For such studies, multiple recessive markers conferring resistance to various drugs, e.g., resistance to emetine (Emtr), thioguanine (Thgr), azaadenine (Azar), phytohemagglutinin (Phar), diphtheria toxin (Dipr), toyocamycin (Toyr), aminopterin (Amnr), and methylglyoxalbisguanyl hydrazone (Mbgr), were introduced into CHO lines by selecting successively for one drug at a time. Hybrids were constructed between the multiply marked lines and the sensitive cells, and segregation frequencies for the various markers, singly and in different pairs, were examined. Results of such studies show that of the recessive markers examined, none cosegregated from the hybrid cells. The independent segregation of the X-chromosome-linked Thgr and of the rest of the markers indicates that none of these other mutations are located on the X chromosome. These results also provide strong suggestive evidence that functional hemizygosity in CHO cells is not restricted to one or a few chromosomal regions, but rather appears to be widespread.

Adenine↗
PubMed1980

DRB resistance in Chinese hamster and human cells: genetic and biochemical characteristics of the selection system.

Stable mutants resistant to the nucleoside analog 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB), which interferes with RNA synthesis, have been selected in Chinese hamster ovary (CHO) and human diploid fibroblasts. In CHO cells, upon treatment with the mutagen ethyl-methane sulfonate (EMS), a linear dose--response between the concentration of mutagen and the frequency of DrbR mutants was observed in the range of 20--300 micrograms/ml. The selection system did not show cell density or cross-feeding effects, and the optimal expression time following mutagenesis was found to be 2--3 days for CHO cells and 5--6 days for human fibroblasts. The DrbR mutation behaved codominantly in DrbR x DrbS hybrids. Addition of DRB affected nucleoside uptake to a similar extent in both wild-type and mutant cells, indicating that the drug was able to enter the mutant cells. The failure of DrbR mutants to show any cross-resistance to other toxic nucleoside analogs examined suggests that the action of DRB does not involve the initial phosphorylation step. DRB addition did not cause any marked inhibition of either RNA polymerase I or RNA polymerase II activity from both wild-type and mutant cells in vitro, indicating that its effect on RNA synthesis may be indirect.

Animals↗
PubMed1980

Diphtheria toxin resistance in Chinese hamster cells: genetic and biochemical characteristics of the mutants affected in protein synthesis.

Diphtheria toxin (DT) resistant mutants (Dipr) have been isolated from a number of different Chinese hamster lines. Among mutants affected in protein synthesis (DiprII class), two distinct phenotypes have been identified. In one class, the entire elongation factor-2 (EF-2) activity becomes resistant to DT-catalyzed ADP-ribosylation (DiprIIa class); these mutants behave recessively upon hybridization with sensitive cells. The second kind of protein synthesis mutants contain nearly normal levels of the ADP-ribosylatable EF-2 activity (DiprIIb class). The hybrids the two types of protein synthesis mutants complement each other indicating that mutations in different genes are responsible for them. While the DiprIIa class of mutants are presumably affected in the EF-2, the lesion in DiprIIb mutants seems to have occurred in a yet unidentified protein synthesis factor. Interesting differences are also observed in the characteristics of mutants that presumably are defective in the entry of toxin into cells (DiprI class).

Adenosine Diphosphate Ribose↗
PubMed1980

Genetic markers for quantitative mutagenesis studies in Chinese hamster ovary cells: characteristics of some recently developed selective systems.

Selection conditions have been optimized in the Chinese hamster ovary (CHO) cell system for a number of genetic markers. The genetic systems studied include resistance to the protein-synthesis inhibitors emetine (Emtr) and diphtheria toxin (Dipr), resistance to methylglyoxalbisguanylhydrazone (Mbgr) which affects polyamine transport, resistance to the nucleoside analogs toyocamycin and tubercidin (Toyr), and resistance to thioguanine (Thgr) and ouabain (OuaR). The optimal expression time following mutagenesis for various markers was between 2 and 6 days. A linear dose--response relationship between the concentration of mutagen (ethyl methanesulfonate) and mutation frequency has been observed over the range of 10--700 micrograms/ml, for all of the above markers except Toyr. The response of these markers to other mutagens such as tritium (3H) decay and ICR-191 show some specificity. Since the response of a number of genetic markers can be studied simultaneously in the CHO system, it should prove very useful for studies of quantitative mutagenesis and in assay systems for mutagen detection.

Animals↗
PubMed1980

Diphtheria toxin resistance in human fibroblast cell strains from normal and cancer-prone individuals.

Mutants resistant to diphtheria toxin (Dipr) have been selected from a variety of human fibroblast cell strains derived from both normal subjects and individuals with known genetic predisposition to cancer such as xeroderma pigmentosum, Fanconi anemia and Bloom's syndrome. Treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) led to a marked increase in the frequency of Dipr mutants in various cell strains. The increase in the frequency of Dipr mutants occurred in a linear dose-dependent manner in response to MNNG and ethyl methanesulfonate, in one of the cell strains examined. The rate of mutation to diphtheria toxin as determined by fluctuation analysis was very similar in various cell strains (1-3 x 10(-7) mutations/cell/generation), except for the strain GM1492 (8.8 x 10(-7) mutations/cell/generation) which is derived from a Bloom syndrome patient.

Anemia, Aplastic↗